Soil available-P Research Articles

Assessment of portable X-ray fluorescence (pXRF) for plant-available nutrient prediction in biochar-amended soils

Portable X-ray Fluorescence probe (pXRF) is a tool used to measure many elements quickly and efficiently in soil with minimal sample preparation. Although this sensing technique has been widely used to determine total elemental concentrations, it has not been calibrated for plant-available nutrient predictions. We evaluated the potential of using pXRF for fast plant-available nutrient quantification. Two experiments were conducted in soils treated with two types of biochars to obtain a practical range of soil pH (5.5 − 8.0) and organic carbon (2.0 − 5.5%). Biochars applied were derived from switchgrass (SGB) and poultry litter (PLB). The first experiment received biochars at application rates up to 8% (w/w) and had no plants. The second experiment had up to 4% of SGB or PLB planted with ryegrass (Lolium perenne). Linear regression (LR), polynomial regression (PolR), power regression (PowR), and stepwise multiple linear regression (SMLR) were the models tested. Regardless of the extraction method, phosphorus (P) showed a strong relationship between pXRF and several laboratory extraction methods; however, K prediction via pXRF was sensitive to the plant factor. The optimum soil available-P corresponding to the maximum P uptake in plant tissues can be assessed with pXRF. The LR was inconsistent for calcium (Ca), sulfur (S), and copper (Cu) and non-significant for magnesium (Mg), iron (Fe), and zinc (Zn). Our results showed that pXRF is applicable to estimate P availability in soils receiving organic amendments. More evaluations are needed with diverse soil types to confirm the findings before using pXRF for fertilizer recommendation.

PENGARUH REVEGETASI TERHADAP SIFAT-SIFAT TANAH PADA LAHAN BEKAS TAMBANG TEMBAGA DI NUSA TENGGARA BARAT

Copper mining activities mainly using open-pit techniques, lead to environmental issues such as overburden waste in waste dump areas that have potential to generate acid mine drainage (AMD), which can decrease soil pH and increase heavy metal toxicity. Reclamation efforts, including revegetation using pioneer plants and cover crops are necessary to restore degraded land in waste dump areas. The aim of this research is to analyze soil physical and chemical properties improvement after revegetation on copper post-mining land as an evaluation and to provide recommendations for future reclamation. The research was carried out by analyzing and interpreting laboratory data from soil observations in revegetation areas for the 2016, 2018, 2019 and 2020 planting years, as well as natural forests belonging to PT. Amman Mineral Nusa Tenggara. Revegetation of copper post-mining land does not show a significant improvement in soil physical properties because improving physical properties takes quite a long time, especially in post-mining areas with heavy structural damage. Soil chemical properties analysis shows that revegetation can increase base saturation (BS), cation exchange capacity (CEC), exch-Ca, exch-Mg, and reduce soil Al saturation. In contrast, soil pH, organic-C, total-N, and soil available-P in the revegetation area did not increase as the revegetation age increased. The effect of revegetation appears to be more significant at the age of 2 to 3 years. However, based on the Tukey test, the age of revegetation mostly does not have a significant effect on enhancing soil chemical properties.

The phoD-Harboring Microorganism Communities and Networks in Karst and Non-Karst Forests in Southwest China

Phosphorous (P) limitation is common not only in tropical rainforest and savanna ecosystems, but also in karst forest ecosystems. Soil phoD-harboring microorganisms are essential in soil P cycles, but very little information is available about them in karst ecosystems. A total of 36 soil samples were collected from two types of forest ecosystems (karst and non-karst) over two seasons (rainy and dry), and the diversity and community structure of soil phoD-harboring microorganisms were measured. The contents of available P (AP), soil total P (TP), microbial biomass P (MBP) and the activity of alkaline phosphatase (ALP) in karst forest soils were higher than those in non-karst forest soils, whereas the contents of CaCl2-P, citrate-P, enzyme-P and the activity of acid phosphatase (ACP) were the opposite. Soil AP content was significantly higher in the rainy season than in the dry season, whereas ALP activity was the opposite. The community structure of phoD-harboring microorganisms was more influenced by forest-type than season. The network connectivity was higher in non-karst forests than in karst forests. Two dominant orders, Burkholderiales and Rhizobiales, were the keystone taxa in these networks in two forests, and their relative abundances were higher in non-karst forests than in karst forests. The microorganic diversity indices (e.g., Shannon–Wiener, Evenness, Richness, and Chao1) were substantially higher in karst than in non-karst forests. These indices were positively correlated with the contents of SOC and TN in the two forests; meanwhile, richness and evenness indices were positively correlated with citrate-P, HCl-P, and TP in non-karst forests. Structural equation modelling results showed that the relative abundance of phoD-harboring microorganisms was mainly influenced by pH and AP, with direct affection of soil AP, pH, and ALP activity, and indirect affection of ALP activity through affecting AP. These findings highlight that the P cycle is mainly regulated by the diversity of phoD-harboring microorganisms in karst forest ecosystems, whereas it is mainly regulated by dominant taxa in non-karst forest ecosystems. In future, regulating the interaction networks and keystone taxa of phoD-harboring microorganisms may be critical to alleviating P limitations in karst forest ecosystems.

Vegetation recovery reshapes the composition and enhances the network connectivity of phoD-harboring microorganisms to promote P availability in a karst ecosystem

Soil phoD-harboring microorganisms can facilitate phosphorus (P) transformation and increase the available P (AP) in P-limited soils; however, the mechanism by which these microorganisms enhance AP throughout the vegetation recovery process of karst ecosystems is poorly understood. Accordingly, this study investigates the effect of vegetation recovery on soil AP and the community composition and network connectivity of phoD-harboring microorganisms to elucidate the mechanism by which phoD-harboring microorganisms enhance soil AP in the four vegetation recovery stages (i.e., grassland, shrubland, shrub-arbor forest, and arbor forest) in a karst ecosystem. Results show that soil total P, AP, and microbial biomass P concentrations, as well as alkaline phosphatase activities, litter and soil nutrients, and plant diversity indices (Shannon–Wiener and Pielou) increase with advancing vegetation recovery. Moreover, the diversity indices (Shannon–Wiener and Simpson) and network complexity of the phoD-harboring microorganisms also increase with advancing vegetation recovery, leading to distinct communities among the four recovery stages. Rhizobiales, Pseudomonadales, and Burkholderiales comprise the dominant phoD-harboring microorganism orders. The relative abundances of Pseudomonadales and Burkholderiales increase with advancing vegetation recovery; Rhizobiales is the highest in shrubland and the lowest in grassland. The structural equation model results show that advanced vegetation recovery is associated with increased plant diversity, litter nutrients, and soil nutrients. The network connectivity is enhanced with advancing vegetation recovery accompanied by increasing soil phosphatase activity and P availability. These results suggest that regulating the phoD-harboring microorganism composition and network connectivity is essential to alleviate plant P limitation in karst ecosystems.

Pervasive soil phosphorus losses in terrestrial ecosystems in China

AbstractFuture phosphorus (P) shortages could seriously affect terrestrial productivity and food security. We investigated the changes in topsoil available P (AP) and total P (TP) in China's forests, grasslands, paddy fields, and upland croplands during the 1980s–2010s based on substantial repeated soil P measurements (63,220 samples in the 1980s, 2000s, and 2010s) and machine learning techniques. Between the 1980s and 2010s, total soil AP stock increased with a small but significant rate of 0.13 kg P ha−1 year−1, but total soil TP stock declined substantially (4.5 kg P ha−1 year−1) in the four ecosystems. We quantified the P budgets of soil–plant systems by harmonizing P fluxes from various sources for this period. Matching trends of soil contents over the decades with P budgets and fluxes, we found that the P‐surplus in cultivated soils (especially in upland croplands) might be overestimated due to the great soil TP pool compared to fertilization and the substantial soil P losses through plant uptake and water erosion that offset the P additions. Our findings of P‐deficit in China raise the alarm on the sustainability of future biomass production (especially in forests), highlight the urgency of P recycling in croplands, and emphasize the critical role of country‐level basic data in guiding sound policies to tackle the global P crises.

Distribution of phosphorus and potassium in selected rice cultivated soils and their accumulation in rice grains under farmer-managed field conditions in Sri Lanka

Rice (Oryza sativa L.) is the staple food in Sri Lanka and phosphorus (P) and potassium (K) are major nutrients for the rice plant. However, the variation of P and K contents (mg kg−1) in rice soils and rice grains as affected by agro-climatic zones (ACZs), water source used (i.e., major irrigation, minor irrigation and rain-fed) and cropping systems adopted (i.e., fallow, vegetable, perennials, other field crops) by Sri Lankan farmers are not well elucidated, and are thus investigated in the present study. A total of 200 rice soil and 230 rice grain samples across the country were collected from farmer fields, representing different ACZs, water sources used, and cropping systems adopted using a stratified random sampling approach. The total and available P and K contents in rice soil, and the P and K contents in rice grains were determined. The plant-available P contents in soil were similar among ACZs, water sources, and rice-based cropping systems. Exchangeable K content was higher in rice fields where vegetables were cultivated in the previous season. Grain P and K contents were similar among the water sources used and rice-based cropping systems. Grain P content was the lowest in the Low country Wet zone. Soil available-P and total-P contents (r = 0.29, p < 0.0001), and grain P and K contents were positively correlated (r = 0.51, p < 0.0001). The knowledge generated in the present study is important in P and K nutrient management in rice cultivation in the country.

Industrial and agricultural waste amendments interact with microorganism activities to enhance P availability in rice-paddy soils

Adding industrial and agricultural wastes to farmland can increase soil available phosphorus (P) pool and boost crop production, but the process affecting soil P transformation and bioavailability is still poorly understood. We studied the effects of straw (ST), biochar (BC) and Si-modified biochar (Si-BC) amendments on the available-P content and its fraction transformation in rice-paddy soils. Our results showed that these three soil amendments significantly increased the concentrations of both microbial biomass carbon (MBC) and microbial biomass-P (MBP) during the first rice season; by contrast, the effects of ST and BC application were relatively poor on acid-phosphatase (ACP) activity, which was increased by 24 % under ST and 14 % under BC. Soil total P concentrations did not differ significantly, although the concentration and percentage of each P-fraction were altered significantly among treatments. Although all three applications increase soil available-P concentration by promoting the transformation of organic-P (Po) components to inorganic-P (Pi), there are differences in the transformation efficiency of the soil P fraction between these amendments. Redundancy analysis results also showed significant clustering of soil P-fraction transformations after ST and BC treatments. Structural equation model analysis further indicated that all amendments regulated microbial processes by changing soil pH and dissolved organic carbon (DOC), thereby promoting soil P transformation and improving P efficiency. Sodium bicarbonate-extractable Po (NaHCO3-Po) contributed most to soil available-P under the different amendments. Compared to ST and Si-BC, BC application improved more soil microbial status and the transformation of soil unavailable-P into available-P, therefore the application of BC in rice fields is the most beneficial method to promote phosphorus use and production sustainability in rice. These findings helped to understand the effects of using industrial and agricultural waste (e.g. straw, biochar and Si-modified biochar) on soil P-fractions and so provided a reference for sustainable resource use and green production in rice-paddy ecosystems.

Dosage effects of organic manure on bacterial community assemblage and phosphorus transformation profiles in greenhouse soil.

Manure is a potential substitute for chemical phosphate fertilizer, especially in intensive agriculture, such as greenhouse farming, but the associations between soil phosphorus (P) availability and the soil microbial community under manure application instead of chemical phosphate fertilizers are still rarely addressed. In this study, a field experiment in greenhouse farming with manure application instead of chemical phosphate fertilizers was established, including five treatments: a control with conventional fertilization and chemical phosphate fertilizer substitution treatments using manure as the sole P resource at 25% (0.25 Po), 50% (0.50 Po), 75% (0.75 Po), and 100% (1.00 Po) of the control. Except for 1.00 Po, all the treatments applied with manure harbored similar levels of available P (AP) as the control. Most of the bacterial taxa involved in P transformation were enriched in manure treatments. Treatments of 0.25 Po and 0.50 Po significantly enhanced bacterial inorganic P (Pi) dissolution capacity, while 0.25 Po decreased bacterial organic P (Po) mineralization capacity. In contrast, the 0.75 Po and 1.00 Po treatments significantly decreased the bacterial Pi dissolution capacity and increased the Po mineralization capacity. Further analysis revealed that the changes in the bacterial community were significantly correlated with soil pH, total carbon (TC), total nitrogen (TN), and AP. These results revealed the dosage effect of the impact of manure on soil P availability and microbial P transformation capacity and emphasized that an appropriate dosage of organic manure is important in practical production.

Metagenomic strategies uncover the soil bioavailable phosphorus improved by organic fertilization in Mollisols

Microorganisms play essential roles in soil phosphorus (P) cycling and the regulation of P bioavailability, however, genetic information on microbial P cycling in response to nutrient inputs is largely unclear. Here, metagenomic sequencing and genome binning were used to investigate microbial functional traits under chemical and organic fertilization in three long-term field experiments across black soil region of Northeast China. The results revealed that manure amendments strongly affected microbial P cycle-related functional gene patterns, which were significantly and positively correlated with the contents of soil total P (TP) and available P (AP). Manure addition directly increased soil AP concentrations, and indirectly acted through the alterations of microbial functional genes involved in soil P cycling. Specifically, manure amendments consistently decreased abundances of phnC gene and increased gene abundances of phnP, opd, and phoN across three locations, suggesting the potentially inhibition of soil microbial P-uptake and transport and the promotion of soil microbial organic P- mineralization. Manure addition promoted microbial inorganic P-solubilization by enriching the ppa, gcd, and pqqC genes at two out of three locations, while chemical fertilizer (CF) addition slightly stimulated the functional gene abundances involved in microbial P-uptake and transport and P-starvation response regulation. In addition, soil AP content was negatively correlated with the phnC gene abundance but positively correlated with the gene abundances of opd and phoN. Moreover, 23 metagenome-assembled genomes (MAGs) were reconstructed covering all soil samples, all of which contained the phnC gene with the copy numbers varying from 1 to 19. Nevertheless, only bin44 had a negative correlation with soil AP (r = −0.361, P = 0.030) and could be considered as a potential indicator regulating microbial P-uptake and transport. Taken together, manure inputs positively accelerated microbial P-transformations, which was beneficial for the establishment of efficient P management strategies in sustainable-intensive agriculture.

Elevational variation in soil phosphorus pools and controlling factors in alpine areas of Southwest China

As an important life element in the Earth’s ecosystem, soil phosphorus (P) is of great significance to stability and sustainable development of terrestrial ecosystems. However, seasonal variations in different soil P pools and their regulatory mechanisms along elevations are not fully understood. Here, we investigated seasonal variations in soil P pools including total P (TP), available P (AP), inorganic P (IP), organic P (OP), labile P, moderately labile P, and stable P in topsoil (0–15 cm) along different elevations (2600–3900 m) in the Yulong Snow Mountain. The associated drivers including leaf nutrient contents, soil properties, micro-climate, and microbial parameters were also examined. We found that all soil P fractions reached a maximum at mid-elevations (2,900 m and 3,200 m), possibly due to the more active microorganisms and suitable soil climatic conditions for advancing P weathering. Meanwhile, soil AP pool was also observed to be tightly related to the leaf P content along elevations. Unexpectedly, most soil P pools did not show seasonal changes, except for AP showing significantly higher level in the wet season than in the dry season, owing to the high temperature and microbial activity for promoting P release in the wet season. Consequently, we found that microbial P, acid phosphatase and dissolved organic carbon had a stronger influence on different P pools than other soil factors. Moreover, there was a strong interaction of labile P and moderately labile P with soil environments (i.e. soil moisture, temperature, dissolved organic carbon). Collectively, our results revealed the elevational shifts in soil P pools and potential mechanisms in Yulong Mountain, and provided an important theoretical basis for soil P dynamics in response to environments in mountain ecosystems.

Penicillium oxalicum augments soil lead immobilization by affecting indigenous microbial community structure and inorganic phosphate solubilization potential during microbial-induced phosphate precipitation

Phosphate-solubilizing microorganisms (PSMs) are critically important for increasing soil phosphate (P) and decreasing lead (Pb) bioavailability during microbial-induced phosphate precipitation (MIPP). However, their relative contributions to the indigenous soil microbial communities and P-cycling genes during the MIPP process remain unclear. In this study, inoculation of the PSM P. oxalicum in hydroxyapatite-cultured and Pb-contaminated soil increased soil phosphatase activities, available P (AP) concentrations and reduced available Pb levels. Metagenomics revealed a 3.9–44.0% increase in the abundance of P-cycling genes by P. oxalicum inoculation. No P-cycling genes were assigned to Penicillium. While P. oxalicum increased the complexity of microbial community co-occurrence networks, and improved the directly interrelationships between Penicillium and genera containing P-cycling gene. These results suggesting that P. oxalicum obviously positively affected the regulation of indigenous P-cycling functional communities during the MIPP process. Inorganic P solubilization genes (gcd, ppa, and ppx) have been shown to affect soil AP, suggesting that inorganic P solubilization is the major driver of Pb immobilization improvement following P. oxalicum inoculation. These results enhance our understanding of the significant ecological role of PSMs in governing soil P-cycling and alleviating Pb2+ biotoxicity during the MIPP process.

Effects of on- and off-year management practices on the soil organic C fractions and microbial community in a Moso bamboo (Phyllostachys edulis) forest in subtropical China.

On- and off-year management practices are usually adopted in Moso bamboo (Phyllostachys edulis) forests to achieve higher productivity. However, little is known about the effects of these management practices on soil C sequestration and microbial community structure. In the present study, soil nutrient content, organic C fractions, and bacterial and fungal communities were comparatively investigated in on- and off-year bamboo stands. The results showed that soil organic C (SOC), alkali-hydrolyzable N (AN), and available P (AP) in the on-year were significantly lower (p ≤ 0.05) than those in the off-year. Among the different soil organic C fractions, easily oxidizable organic C (EOC), microbial biomass C (MBC), Ca-bound SOC (Ca-SOC), and Fe/Al-bound SOC (Fe/Al-SOC) also had significantly higher contents in the off-year than in the on-year, with MBC and EOC decreasing by 56.3% and 24.5%, respectively, indicating that both active and passive soil organic C pools increased in the off-year. However, the alpha diversities of both soil bacteria and fungi were significantly lower in the off-year soils than in the on-year soils. The bacterial taxa Actinobacteria, Planctomycetes, WPS-2, Acidothermus, Candidatus_Solibacter, Burkholderia-Caballeronia-Paraburkholderia, and Candidatus_Xiphinematobacter were increased in off-year soils relative to on-year soils. Meanwhile, fungal taxa Ascomycota, Mortierella, Hypocrea, Cryptococcus, Clitopilus, and Ceratocystis were significantly increased in on-year soils. Soil pH, SOC, AP, MBC, EOC, and Ca-SOC were significantly correlated with bacterial and fungal communities, with soil pH being the most important driving factor for the shift in bacterial and fungal communities. Our findings showed that the studied bamboo forest possessed an inherent restorative ability in the off-year, which can reverse the soil nutrient and C depletion in the on-years and ensure soil fertility in the long term.

Coated diammonium phosphate combined with Paecilomyces variotii extracts improves root architecture, enhances spring low temperature tolerance, and increases wheat yield

The growth, development, and grain yield of winter wheat (Triticum aestivum L.) was seriously limited by the low use efficiency of phosphorus (P) fertilizers and the spring low-temperature events. Diammonium phosphate is one of the most important sources of P fertilizers worldwide. Controlled release diammonium phosphate (CRDAP) synchronizes fertilizers P release and crop growth demand is positive to improve P use efficiency (PUE) and reduce P loss, whereas biostimulants such as Paecilomyces variotii extracts (ZNC) have ultrahigh activity in promoting crop growth and abiotic stress resistance. However, little information is available on synergistic effects of CRDAP and ZNC on winter wheat growth. A three-year field experiment from October 2017 to June 2020 was conducted with five treatments: DAP (application of conventional diammonium phosphate); CDAP (CRDAP application); DAPZ (application of diammonium phosphate–ZNC composite); CDAPZ (application of CRDAP–ZNC composite); Control (no P fertilizer or ZNC). Plant growth (root, shoot, and photosynthesis), hormone (auxin content from roots and leaves, and ABA content from leaves), ROS scavenging system (H2O2, superoxide dismutase (SOD), peroxidase (POD), catalase (CAT), and glutathione reductase (GR)), and soil available P were measured along with yield and PUE. The results showed that the yield and PUE of CDAPZ were significantly more (by 6.0% and 9.3 percentage points, respectively) than for CDAP. The interactive effects between CRDAP and ZNC were evidenced by the CDAPZ enhanced soil available-P supply and increased average available-P content (22.0% more than CDAP in the 0–40 cm soil layer) and improved root growth with 29.9% increase in total root length by CDAPZ than CDAP at the jointing stage. Moreover, the IAA content of roots from CDAPZ was higher than any other treatments, and the effect of ZNC on IAA content was verified by a laboratory incubation experiment. Similarly, the highest photosynthetic rate was found in CDAPZ, which was 11.0–17.0% higher than that in CDAP. The application of CRDAP combined with ZNC decreased H2O2 content by 8.6%, and increased the activities of SOD, POD, CAT, and GR, thereby enhancing the cold tolerance of wheat. Hence, CRDAP–ZNC composite may serve as an emerging green fertilizer technology and play a crucial role in improving crops response to climate change, and increasing crop yield and PUE.

The Contributions of Soil Biochemical Properties as Determinant of Pineapple (Ananas comosus [L.] Merr.) Plantation LandProductivity in Central Lampung Regency

One of the management challenges in pineapple cultivation at plantation scale is the still occurrence of disparity in land productivity across the cultivated area although the cropping practices have been implemented for many years. In the case of a pineapple plantation in Central Lampung Regency, contribution of soil biochemical properties in terms of various soil enzyme activities as a determinant factor of land productivity has never been elaborated. This research was aimed to study the relationships among biochemical and other soil properties with land productivity or pineapple yield at plantation scale. Rhizosphere soil-composite samples were taken purposively from 4 stations at the largest Indonesian pineapple plantation representing blocks with high and low yield and growth at vegetative and generative phase. Relationships amongst the studied parameters were evaluated using PCA and linear multiple regression analysis. The results showed significant contributions of the rhizosphere soil properties on the pineapple yield according to equation: Yield = 64.895 – 6.546 PCA1 +13.057 PCA2 – 7.722 PCA4 (R2= 0.612), where PCA1 consisted of soil available-P, available-K, and CEC; PCA2 was of soil base saturation, total microbe population, enzyme activities of cellulase and invertase, while PCA4 was of soil organic C, silt fraction, and phosphatase activities.

Metagenomic insights into the effects of organic and inorganic agricultural managements on soil phosphorus cycling

Microbes play important roles in regulating soil phosphorus (P) cycling in agroecosystems. However, little is known about how P-cycling microbes respond to organic and inorganic agricultural managements in terms of their functional and phylogenetic traits. Here, metagenomics was used to determine effects of P-cycling functional genes and taxa on soil P availability in a forage (Broussonetia papyrifera) monoculture ecosystem under organic (inoculating arbuscular mycohrrizal fungi (AMF) and intercropping legume (Medicago sativa)) and inorganic (adding chemical nitrogen (N) and P fertilizers) managements. The results showed that soil available P (AP) in plots with both legume and AMF addition was increased by 54.3 % compared with the control and was1.6–2.4 times higher than in plots with N or P fertilization. The abundance of ppa involved in inorganic-P solubilization was significantly increased after adding both legume and AMF compared with P-addition treatment. Soil alkaline phosphatase activity increased with P fertilizer addition and was positively correlated with soil AP. The abundances of phoA and phnI involved in organic-P mineralization were significantly higher under P fertilization treatment than under N fertilization treatment. Soil total N and AP were the key drivers on interactions among P-transportation genes, organic-P mineralization genes and taxa related to P-transportation. Overall, organic agricultural management increases soil P availability by increasing the potential of inorganic-P solubilization, while inorganic agricultural management regulates P availability via altering the potential of organic-P mineralization. These findings could provide a better understanding of the mechanisms that drive soil P availability under organic and inorganic agricultural managements.

Long-term high-P fertilizer input shifts soil P cycle genes and microorganism communities in dryland wheat production systems

Phosphorus (P) fertilizer input influences crop yield, soil P cycling, and phosphate-solubilizing microorganism (PSM) communities, which play a key role in obtaining soil available phosphorus. However, the responses of soil P cycle genes and PSM communities to long-term high-P fertilizer application are less known in the Chinese Loess Plateau. In this study, metagenomics was used to explore the shifts in the abundance and compositions of soil P cycle genes and PSM communities at a long-term (14 years) trial site with four P fertilization rates. Long-term high-P (200 kg P2O5 ha−1 year−1) inputs resulted in a decrease in the abundance of the P-starvation response genes (phoR and phoP), the high-affinity phosphate-specific transporter (pst), the inorganic P-solubilization, and organic P-mineralization genes (gcd, pqq, and phoD). Long-term P inputs increased the abundance of phosphate-solubilizing bacteria but decreased the abundance of phosphate-solubilizing fungi and weakened the relationship of relevant key soil P genes. Soil total P, inorganic P, available P (AP), dissolved organic C contents, and alkaline phosphatase (ALP) activity were significantly related to soil P cycle genes and PSM community structure. In conclusion, the changes in soil P cycle genes and microbial P solubilization capacity under long-term P input conditions were mainly regulated by soil AP content and ALP activity, while long-term high-P inputs increased soil mineral P immobilization by altering the expression of soil P cycle genes and the PSM functional profiles. These consequences provide a new view for the study of soil P cycles in agricultural ecosystems with P inputs.

N addition alters growth, non-structural carbohydrates, and C:N:P stoichiometry of Reaumuriasoongorica seedlings in Northwest China

Reaumuria soongorica is an important biological barrier for ecological protection in the Gobi Desert in northwestern China, where soil nitrogen availability is low. N deposition has recently increased significantly in Gobi Desert, and the responses of R. soongorica to N enrichment may become a problem for ecological restoration and protection. However, little is known about the effects of N addition on the biomass, non-structural carbohydrates (NSC), and carbon:nitrogen:phosphorus (C:N:P) stoichiometry of R. soongorica in this region. Here, we examined changes in biomass, NSC and C:N:P ratios of different organs of R. soongorica seedlings in four N addition treatments: 0 (N0), 4.6 (N1), 9.2 (N2), and 13.8 (N3) g m−2 year−1. N addition up to 9.2 g m−2 year−1 significantly increased the biomass of different organs, simultaneously increasing the belowground: aboveground ratio of R. soongorica seedlings. Root NSC concentrations significantly increased under all N addition treatments, but leaf and stem NSC concentrations only increased under the N1 and N2 addition treatments. Nitrogen addition enhanced the soluble sugar concentrations (SSC) of leaves and roots, and reduced starch concentrations (SC) of all organs. Stem and root N concentrations significantly increased under the N2 and N3 treatments, and leaf N concentrations only increased under the N3 treatment, but N addition had no significant effect on plant C and P concentrations. Leaf and stem C:N ratios decreased significantly under the N2 and N3 treatments, but root C:N decreased significantly in all N addition treatments. The N3 treatment significantly increased the N:P ratio of all organs. N addition significantly enhanced available N (AN), available P (AP) and total phosphorus (TP) in rhizosphere soil. Our results suggest that N addition alters the biomass, NSC, N concentrations, C:N and N:P ratios of all plant organs, but roots responded more strongly than stems or leaves to N addition, potentially allowing the plants to absorb more water from the arid soil in this region ensuring the survival of R. soongorica seedlings. Rhizosphere soil AP, AN and TP concentrations were important factors affecting the NSC concentrations and stoichiometric characteristics of R. soongorica.

Long-term phosphorus addition inhibits phosphorus transformations involved in soil arbuscular mycorrhizal fungi and acid phosphatase in two tropical rainforests

Increasing atmospheric nitrogen (N) and phosphorus (P) deposition affect soil nutrient availability and biogeochemical cycles, yet the impacts on the regulatory processes of soil P in P-poor tropical rainforests are not well understood. Based on a ten-year N and P addition experiment in primary and secondary rainforests in Hainan, China, we investigated the effects of N and P additions on four soil P fractions, acid phosphatase (ACP) activity, kinetic characteristics and arbuscular mycorrhizal (AM) diversity. Our results showed that P addition significantly increased soil available P (AP), but had no significant effects on microbial P and microbial N:P ratio in both rainforests. Late-successional primary rainforest had higher microbial P and lower N:P ratio compared to early-successional secondary rainforest, suggesting that forest succession would not aggravate microbial P limitation. Plants and microorganisms accessed most inorganic P by releasing hydrion and organic acids to mobilize soil P, whereas inorganic P accessed by root interception and organic P readily mineralized by ACP and phytase enzymes were relatively low. In the primary rainforest, ACP and kinetic parameters were significantly increased under low N addition, while P addition remarkedly declined ACP activity and AM diversity in both rainforests. Additionally, CaCl2 extractable P, citrate extractable P, and HCl extractable P in the two forests were significantly positively associated with soil AP, but negatively associated with ACP activity, kinetic parameters and AM diversity. Therefore, the transformations of organic P were inhibited after the exogenous addition of inorganic P. Overall, our study evaluates the soil P acquisition strategies and regulatory processes in tropical rainforests with different successional stages, which can be used to predict the effects of long-term N and P deposition on soil P cycling in P-poor tropical rainforests.

Okra Growth, Yield and Rhizosphere Microbiome Responses to the Encapsulated Bioinoculant Application under Reduced Fertilization Regime.

Simple SummaryIn the present study, a novel strain of Enterobacter hormaechei, strain 40a, was evaluated as a bioinoculant for greenhouse-grown okra cultivation. The strain 40a was used in both free-cell and encapsulated form (alginate beads containing sugar-protein hydrolysate and molasses) in combination with different phosphate (P) and potassium (K) fertilization dosages. According to the findings, strain 40a enhanced the amount of P and K that was available in the soil as well as the number of culturable bacteria. This increased the okra’s overall growth qualities, P and K content, and productivity. Additionally, strain 40a altered the rhizosphere’s bacterial structure, resulting in a high abundance of bacteria that are favourable to plants, and enhanced soil qualities. Interestingly, okra displayed equal growth increase in both biweekly free-cell strain 40a and one-time encapsulated strain 40 treatments. This shows that encapsulated bioinoculant could be a low-cost farming option in precision agriculture.There is limited evidence that Enterobacter hormaechei can improve plant physiology and yield through soil phosphate (P) and potassium (K) amelioration. This study unraveled the effect of different soil inoculation methods i.e., free-cell and encapsulated (alginate bead containing sugar-protein hydrolysate and molasses) E. hormaechei 40a with different rates of PK-fertilization on okra P and K uptake, and soil rhizosphere bacterial community. The results revealed that 3HB (half-dose PK-fertilizer + encapsulated strain 40a) had the highest soil available P (SAP) and K (SAK), as well as P and K uptake for all plant organs, followed by 3F (full-dose PK-fertilizer), 3HI (half-dose PK-fertilizer + free-cell strain 40a), and 3H (half-dose PK-fertilizer), and improved yield by up to 75.6%. Both inoculated and full-dose fertilizer treatments produced larger pods (>15 cm) compared to 3H. We discovered increased bacterial richness and diversity in both 3HB and 3HI samples compared to uninoculated treatments. Both 3HB and 3F treatments were positively correlated with the increasing abundance of Acidobacteriales, Burkholderia caballeronia paraburkholderia, Gemmataceae, and Sphingomonas along with the SAP and SAK. The plant-beneficial effect of one-time 3HB treatment on okra growth and yield was comparable to biweekly inoculation in 3HI, suggesting a new cost-effective farming approach in precision agriculture.

Effect of Coated Diammonium Phosphate Combined with Paecilomyces variotii Extracts on Soil Available Nutrients, Photosynthesis-Related Enzyme Activities, Endogenous Hormones, and Maize Yield

Coated diammonium phosphate (CDAP) is intended to release nutrients steadily in response to the demand of crop growth. A novel biostimulant extracted from Paecilomyces variotii has been shown to regulate gene expression in nutrient transport, enhance nitrogen (N) and phosphorus (P) uptake, and improve nutrient use efficiency. The application of CDAP combined with the Paecilomyces variotii extracts (ZNC) in maize is an efficient approach for reducing waste of resources, improving nutrient supply, and maintaining production stability. The effects of CDAP combined with ZNC on photosynthesis, enzyme activities, endogenous hormone content, maize yield, and P use efficiency (PUE) were investigated in this study. In a pot experiment, CDAP and diammonium phosphate (DAP) were tested together with P levels (1.80, 1.44 g pot–1, P2O5) and two ZNC application rates (0, 4.4 μg pot–1), which included the control treatment that had no P fertilizer added. Results showed that the key influencing elements of maize growth and yield were the soil available-P content, endogenous hormone content, and plant photosynthesis in this study. The combination of DAP and ZNC increased the soil available-P content and the auxin content in leaves at the key stage and hence increased the yield and PUE of maize, compared with DAP. The net photosynthetic rate of CDAP combined with ZNC was higher by 23.1% than that of CDAP alone, as well as by 32.0% than that of DAP combined with ZNC. Moreover, the combination of CDAP and ZNC increased the yield and PUE by 8.2% and 15.6 percentage points compared with DAP combined with ZNC while increasing the yield and PUE compared with CDAP. In conclusion, combining CDAP with ZNC as an environmentally friendly fertilizer could improve photosynthesis-related enzyme activity and enhance the net photosynthetic rate, resulting in an increase in maize yield and PUE significantly.